Oximetry screening (pulse oximetry), a rapid, non-invasive test that measures levels of oxygen in the blood of newborn babies is better at detecting cases of congenital heart defects than current screening techniques involving a mid-trimester ultrasound scan and a routine physical exam soon after birth, researchers reported in The Lancet. The authors added that pulse oximetry should be used routinely on all newborns. With pulse oximetry, a sensor is placed on the baby's hand or foot. It is a quick and inexpensive test.